今天进行之前某个项目的优化,发现自己当时对数据库的操作采用了Apache的DBUtils框架,导致存在大量的像获取connection、获取statement、获取resultset、遍历resultset并封装成集合、依次关闭connection,statement,resultset等这些重复操作。这样的代码简直不能忍。基于使用的框架是spring,于是决定使用spring jdbctemplate改写。但是在applicationContext.xml中配置完DataSource后,脑袋一片空白, 忘记如何获取想要的bean。查询资料后发现竟然有七种方式之多(用了这么久的spring框架,竟然一种方法没想到。。为此感到羞愧)。特此总结下来以便日后查阅。
本文不涉及自动注入等方式.
- 在初始化时保存ApplicationContext对象
ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
BasicDataSource bds1 = (BasicDataSource) context.getBean("ds");
ApplicationContext ac = new FileSystemXmlApplicationContext("applicationContext.xml");
BasicDataSource bds2 = (BasicDataSource)ac.getBean("ds");
- 这种方式实例化applicationContext是非常耗时的,适用于采用Spring框架的独立应用程序,仅仅推荐使用在程序需要通过配置文件手工初始化Spring的情况。ApplicationContext的主要实现类是ClassPathXmlApplicationContext和FileSystemXmlApplicationContext,前者默认从类路径加载配置文件,后者默认从文件系统中装载配置文件。
(1)、FileSystemXmlApplicationContext
这个方法是从文件绝对路径加载配置文件,例如:
ApplicationContext ctx = new FileSystemXmlApplicationContext( "C:/applicationcontext.xml ");
如果在参数中写的不是绝对路径,那么方法调用的时候也会默认用绝对路径来找。
classpath路径,需要加入前缀classpath: )
(2)、ClassPathXmlApplicationContext
这个方法是从classpath下加载配置文件(适合于相对路径方式加载),例如:
ApplicationContext ctx = new ClassPathXmlApplicationContext( "/applicationcontext.xml ");
classpath: 前缀是不需要的,默认就是指项目的classpath路径下面;这也就是说用ClassPathXmlApplicationContext时默认的根目录是在WEB-INF/classes下面,而不是项目根目录。这个需要注意!
通过spring提供的工具类获取
ApplicationContext ac1 = WebApplicationContextUtils.getWebApplicationContext(request.getSession().getServletContext());
BasicDataSource bds4 = (BasicDataSource)ac1.getBean("ds");
ApplicationContext ac2 = WebApplicationContextUtils.getRequiredWebApplicationContext(request.getSession().getServletContext());
BasicDataSource bds = (BasicDataSource)ac2.getBean("ds");
- 通过javax.servlet.ServletContext 获取到ApplicationContext实例对象,这意味着,必须使用到request、session等等。上面两个工具方式的区别是,前者在获取失败时抛出异常,后者返回null。当使用WebApplicationContextUtils获取ApplicationContext实例时,需要在web.xml配置文件中添加org.springframework.web.context.ContextLoaderListener监听器,否则获取不到ApplicationContext对象,返回Null。web.xml配置示例如下:
<context-param>
<param-name>contextConfigLocation</param-name>
<param-value>classpath:applicationContext.xml</param-value>
</context-param>
<listener>
<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>
- 实现接口ApplicationContextAware
实现该接口的setApplicationContext(ApplicationContext context)方法,并保存ApplicationContext 对象。Spring初始化时,会通过该方法将ApplicationContext 对象注入。
package Util;
import org.springframework.beans.BeansException;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.stereotype.Component;
//@Component
public class SpringContextUtil implements ApplicationContextAware {
// Spring应用上下文环境
private static ApplicationContext applicationContext;
/**
* 实现ApplicationContextAware接口的回调方法,设置上下文环境
*
* @param applicationContext
*/
public void setApplicationContext(ApplicationContext applicationContext) {
SpringContextUtil.applicationContext = applicationContext;
}
/**
* @return ApplicationContext
*/
public static ApplicationContext getApplicationContext() {
return applicationContext;
}
/**
* 获取对象
*
* @param name
* @return Object
* @throws BeansException
*/
public static Object getBean(String name) throws BeansException {
return applicationContext.getBean(name);
}
}
- 通过BeanFactory接口获得Bean
新建一个类,不过该类需要实现BeanFactoryAware接口,该接口有一个方法public void setBeanFactory(BeanFactory beanFactory) throws BeansException;该方法是为了设置BeanFactory对象,系统会在启动的时候自动设置BeanFactory。具体代码如下:
package Util;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.BeanFactoryAware;
public class SpringBeanFactoryUtils implements BeanFactoryAware {
private static BeanFactory beanFactory = null;
private static SpringBeanFactoryUtils factoryUtils = null;
public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
SpringBeanFactoryUtils.beanFactory = beanFactory;
}
public static BeanFactory getBeanFactory() {
return beanFactory;
}
public static SpringBeanFactoryUtils getInstance(){
if(factoryUtils==null){
//factoryUtils = (SpringBeanFactoryUtils)beanFactory.getBean("springBeanFactoryUtils");
factoryUtils = new SpringBeanFactoryUtils();
}
return factoryUtils;
}
public static Object getBean(String name){
return beanFactory.getBean(name);
}
}
- 不过应该注意的是,该类中有一个getInstance方法,目的是利用单例模式获得该类的一个实例,但由于getBean(String name)方法是静态的,所以用不用单例都无关紧要,经过测试,两种方法都行的通。另外一点就是必须把该类添加到applicationContext.xml的配置文件中<bean id="springBeanFactoryUtils" class="Util"/>
通过Spring提供的ContextLoader
WebApplicationContext wc = ContextLoader.getCurrentWebApplicationContext();
BasicDataSource bds = (BasicDataSource)wc.getBean("ds");
继承自抽象类ApplicationObjectSupport
package com.controller;
import javax.servlet.ServletContext;
import javax.servlet.http.HttpServletRequest;
import org.apache.commons.dbcp.BasicDataSource;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ApplicationObjectSupport;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import org.springframework.context.support.FileSystemXmlApplicationContext;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.context.ContextLoader;
import org.springframework.web.context.WebApplicationContext;
import org.springframework.web.context.support.WebApplicationContextUtils;
import Util.SpringBeanFactoryUtils;
import Util.SpringContextUtil;
@Controller
public class TestController extends ApplicationObjectSupport{
@RequestMapping("/test6.do")
public String test6(HttpServletRequest request) {
ApplicationContext ac = getApplicationContext();
BasicDataSource bds = (BasicDataSource)ac.getBean("ds");
System.out.println("6-"+bds.getMaxActive());
return "NewFile";
}
}
- 继承自抽象类WebApplicationObjectSupport
package com.controller;
import javax.servlet.http.HttpServletRequest;
import org.apache.commons.dbcp.BasicDataSource;
import org.springframework.context.ApplicationContext;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.context.support.WebApplicationObjectSupport;
@Controller
public class TestController2 extends WebApplicationObjectSupport{
@RequestMapping("/test7.do")
public String test7(HttpServletRequest request) {
ApplicationContext ac = getApplicationContext();
BasicDataSource bds = (BasicDataSource)ac.getBean("ds");
System.out.println(bds.getMaxActive());
return "NewFile";
}
}
第三、四种方法都需要将工具类配置在Spring配置文件中:
假定ApplicationTool为继承或者实现了第三、四种方法的具体实现类
<bean class="util.ApplicationTool"></bean>
否则将获取不到ApplicationContext,返回Null.